add ability for ribbon/eureka to use ipAddr instead of hostName configed...

add ability for ribbon/eureka to use ipAddr instead of hostName configed via Archaius

this relates to the discussion on the mailing list here:

https://groups.google.com/forum/#!topic/eureka_netflix/7M28bK-SCZU
This method must be called in loadDefaultValues() otherwise it is not useful.